This proposal aims to the development of a new class of high performance nanophotonic scintillators for X-ray imaging. Specifically, the goals of the proposed research are: (1) to develop and optimize transparent glass-matrix scintillator plates (2.5x2.5cm, d1mm in thickness) embedded with Tb3+ or Ce3+, Tb3+ co-doped gadolinium halide or lanthanum halide nanophosphors with a ratio up to 70wt%, (2) to design and construct PC lattice structures on the scintillator plate (2x2 mm localized area), and (3) to investigate ther X-ray imaging performance and compare to existing materials. The new nanophotonic scintillators will be significantly better than existing micron-sized phosphor screens in terms of spatial resolution and light output efficiency. Nanophotonic scintillator based X-ray converting plates should be very useful in biomedical imaging, including mammography and digital radiography. They also promise to have other valuable applications for protein crystallography detectors used at synchrotron beamlines, enhancing their value to NIH and to the molecular biology community as a whole. Phosphor screens made from micron-sized phosphors are efficient and bright X-ray converters. However, large-sized phosphor particles give rise to a great deal of scatter, which limits their spatial resolution, and prevents light propagation and thus decreases efficiency in thicker screens. There is ample theoretical and experimental argument to suggest that nanophosphors in a transparent glass matrix will exhibit significantly better spatial resolution than micron-sized phosphor particles. Also, glass-matrix scintillators ar chemically and mechanically stable, and can be easily shaped into large-area plates for applications in adverse environment. With PC lattice structures patterned on one or both sides of the glass-matrix nanocomposite scintillator, light propagation in the glass plate will be directionally controlled and internal reflection can be virtually eliminated. With significantly enhanced light out-coupling and controlled emission direction (normal to the plate) from the scintillator plate, light collection efficiency will be dramatically increased in the coupling optis such as fiber arrays in a digital X- ray detector. Also, the spatial resolution of such scintillato will be greatly enhanced due to the perpendicular light emission, and will be particularly valuable for high resolution medical imaging. We believe this nanophotonic scintillator will make better X-ray scintillating screens than those currently in use.